The present invention relates to the field of wireless communication, and more specifically relates to uplink transmission in a packet service wireless communication system.
Packet services in a wireless communication network have a very bursty source of traffic. They need to have a very fast access to radio resources and transmit with a high bit rate. For packet services, since the traffic is bursty and the radio resource limited, allocating resources to the different users on a permanent basis is hardly feasible. Thus, at any given time, the network usually needs to control multiplexing of all packet users, in order to avoid overload situations; overload may occur if too many users become active at the same time with a high transmission rate. The problem is especially critical for uplink transmission in packet service, because users transmit in an uncoordinated way, according to their traffic source behaviour.
This problem is for instance discussed in EP-A-0 877 512 in the case of a CDMA (code division multiple access) based mobile communication system. The solution proposed in this document is to broadcast mobile access control information from the base station to the mobile stations. Mobile stations then transmit packet to the base station according to the timing information defined in the broadcast mobile access control information.
This solution is difficult to carry out for high bit rate communications; indeed, the base station has to manage the timing of all mobile stations, which is time consuming. In addition, broadcasting the proposed mobile access control information will also use part of the available radio resource.
WO-A-97 19525 discusses a TDMA (time division multiple access) system, according to the GSM/GPRS specification. This document discusses the use of control algorithms to modify access probabilities. One prior art solution discussed in this document is that the base station broadcasts a value p, and that any ready user transmits with a probability p during any available access burst period. In order to provide different grades of services to different classes of users, this documents suggests broadcasting different probabilities for different groups of users. Any user may select the timing of its transmission based on the broadcast probability for his group. Alternatively, access may be allowed or not in a given allowed burst period according to the comparison of a random number to the broadcast probability.
This document does not discuss CDMA-type systems, and does not suggest the use of a similar process for accessing different resources.
The problem of access to the radio resource, especially for uplink transmission was also discussed for UMTS specification (Universal Mobile Telephone Service). xe2x80x98UMTS YY.03, description of UE states and procedures in connected modexe2x80x99, version 0.4.0, Tdoc SMG2 UMTS L23 61/99 suggests allocating dedicated channels (or DCH) to packet user, and allowing the users to transmit when they wish to. The UTRAN (UMTS Radio Access Network) may control transmission bit rate of each individual UE (User Equipment) on a slow rate basis through a RRC (Radio Resource Control) procedure. This solution results in a sub-optimal usage of radio resources and extra delay at each transmission, because resource allocation is controlled on a too slow basis. Indeed, the time necessary for sending a message from the UTRAN to the UE may reach 200 ms. Collisions can not be avoided and this may lead to a large retransmission overhead. This scheme will probably prevent packet users from transmitting at high bit rate.
Another solution for UMTS is discussed in xe2x80x98Benefits of the uplink shared channel USCHxe2x80x99, Tdoc SMG2 UMTS L23 47/99, Motorola. According to this scheme, users are allocated a DCH but a fast signalling message in downlink indicates them what bit rate to use at every frame. This solution requires too much signalling overhead, especially for a CDMA system which does not require explicit assignment of physical resources.
xe2x80x98Performance of a joint CDMA/PRMA protocol for mixed voice/data transmission for third generation mobile communicationxe2x80x99, A. E. Brand, A. H. Aghvami, IEEE Journal on selected areas in communications, vol.14, No9, December 1996 suggest an uplink protocol for mobile communication systems. According to this protocol, a permission probabilities are sent on each downlink packet, for different slots of the next frame. Permission probability for a slot in a given frame is set according to the periodic load in the same slot of the previous frame.
This solution discusses simultaneous periodic and random loads, and suggests setting permission probabilities according to periodic load only. It is therefore not adapted to controlling packet service uplink transmission.
The invention provides a solution to contention of user equipment or mobiles stations for packet service uplink transmission in a CDMA wireless communication network. It provides a simple and efficient solution for lowering interference, and for optimising use of the radio resource.
More specifically, the invention provides a process for sharing radio resources between user equipments on the uplink of a packet service wireless communication system, comprising:
in the network, computing a maximum transmission rate for user equipments, and broadcasting this maximum transmission rate to user equipments;
in a user equipment, transmitting with a transmission rate lower that the last received broadcast maximum transmission rate.
Preferably, the maximum transmission rate is broadcast every frame.
In one embodiment of the invention, the maximum transmission rate is identical for all user equipments.
In another embodiment of the invention, the maximum transmission rate is class dependent.
The process may also comprise:
in the network, computing a probability for user equipments, and broadcasting this probability to user equipments;
in a user equipment, transmitting only if a random value is lower than the last received broadcast probability.
Preferably, the process comprises:
in the network, computing a probability for user equipments, and broadcasting this probability to user equipments;
in a user equipment, if the requested transmission rate is lower than the broadcast transmission rate, computing a user probability higher than the last received broadcast probability, as a function of the last received broadcast probability, of the last received broadcast maximum transmission rate and of the transmission rate required by the user equipment, and transmitting only if a random value is lower than the last computer user probability.
In one embodiment of the invention, the probability is broadcast every frame.
In another embodiment of the invention, the probability is identical for all user equipments.
In yet another embodiment, the probability is class dependent.
Preferably, the step of transmitting is carried out for a validity time period after it is determined that the random value is lower than the last received broadcast probability.
In another embodiment, a user equipment is not allowed to transmit for a retry time period after it is determined that the random value is not lower than the last received broadcast probability.
In one embodiment of the invention, the step of transmitting is started at a first transmission rate for a time period, and is continued at a second transmission rate after the lapse of said time period.
In this case, the maximum transmission rate may be broadcast to user equipments transmitting at said first transmission rate.
It is also possible for the maximum transmission rate to be broadcast only when it is computed anew.
The invention also provides a wireless communication system carrying out this process, and a user equipment carrying out the user side steps of the process.
A wireless communication system embodying the invention will now be described, by way of non-limiting example, and in reference to the accompanying drawings, where:
FIG. 1 is a flowchart of the procedure in the UTRAN according to a first embodiment of the invention;
FIG. 2 is a flowchart of the procedure in the UE according to the first embodiment of the invention;
FIG. 3 is a representation of the timing of the packet admission control according to the first embodiment of the invention;
FIG. 4 is a flow diagram between UTRAN and UE according to the first embodiment of the invention;
FIG. 5 is a graph of a possible probability function;
FIG. 6 is a flowchart of the procedure in the UTRAN according to a second embodiment of the invention;
FIG. 7 is a flowchart of the procedure in the UE according to the second embodiment of the invention;
FIG. 8 is a flow diagram between UTRAN and UE according to the second embodiment of the invention;
FIG. 9 is a representation of the timing of the packet admission control according to the second embodiment of the invention;